JP6311683B2 - Iron-air battery electrolyte and iron-air battery - Google Patents

Description

  The present invention relates to an electrolytic solution for an iron-air battery and an iron-air battery.

An air battery using oxygen as an active material has many advantages such as high energy density. As an air battery, metal air batteries, such as an iron air battery and an aluminum air battery, are known, for example.
As a technique related to such an air battery, for example, Patent Document 1 discloses an iron-air battery including a positive electrode (air electrode), an electrolyte, and a negative electrode containing iron metal.

JP2012-094509A

Bui Thi Hang, 5 others, “Jonal of Power Sources”, 2006, 155, p. 461-469

However, since the surface of the iron negative electrode used for an iron-air battery is usually covered with an oxide film (passive film), there is a problem that it is inactive as a battery electrode. In order to remove the passive film, a reduction treatment is usually performed before discharge. Thereby, the surface of an iron negative electrode is activated.
However, there is a problem in that it is difficult to obtain a discharge capacity because the surface of the iron negative electrode is repassivated immediately after the reduction treatment due to the influence of dissolved oxygen, hydroxide, etc. in the electrolytic solution.
In order to prevent repassivation of the iron negative electrode surface, Patent Document 1 states that by adding potassium sulfide (K ₂ S) to the electrolytic solution, it is possible to suppress the decrease in the activity of the electrode and promote the discharge reaction. It is disclosed.
However, when an electrolyte containing K ₂ S is used, the discharge capacity of the iron-air battery can be improved. However, if the concentration of K ₂ S changes, the discharge capacity changes greatly. In order to obtain this, there is a problem that high-precision density control is necessary.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide an iron-air battery electrolyte that can improve the discharge capacity of an iron-air battery without performing concentration control, and An iron-air battery using an electrolytic solution is provided.

The electrolytic solution for an iron-air battery of the present invention comprises a discharge reaction accelerator containing at least one anion selected from the group consisting of SCN ^- anions, S ₂ O ₃ ^2- anions, and (CH ₃ ) ₂ NCSS ^- anions. Consisting of an aqueous solution containing
The content of the discharge reaction accelerator is 0.005 mol / L or more and 0.1 mol / L or less, and is used for an iron-air battery having a negative electrode containing an iron element.

In the electrolytic solution for an iron-air battery of the present invention, the discharge reaction accelerator is at least selected from the group consisting of Li ⁺ cation, K ⁺ cation, Na ⁺ cation, Rb ⁺ cation, Cs ⁺ cation, and Fr ⁺ cation. It preferably contains one kind of cation.
In the electrolytic solution for an iron-air battery of the present invention, the discharge reaction accelerator is preferably Na ₂ S ₂ O ₃ .
In the electrolytic solution for an iron-air battery of the present invention, the aqueous solution is preferably basic.
In the electrolytic solution for an iron-air battery of the present invention, the aqueous solution preferably contains KOH as an electrolyte compound.

The iron-air battery of the present invention includes an air electrode to which oxygen is supplied,
A negative electrode containing iron element;
An electrolyte solution in contact with the air electrode and the negative electrode,
The electrolytic solution is the iron-air battery electrolytic solution.

  According to the present invention, it is possible to provide an iron-air battery electrolyte capable of improving the discharge capacity of the iron-air battery without performing concentration control, and an iron-air battery using the electrolyte.

It is sectional drawing which shows schematic structure of the iron air battery of this invention.

1. Iron air battery electrolyte solution of iron air battery electrolyte present invention, SCN ^- _anion, S ^{₂ O 3 2-} anions, _{and, (CH} 3) 2 NCSS ^- at least one anion selected from the group consisting of anionic It consists of the aqueous solution containing the discharge reaction accelerator containing, and is used for the iron air battery which has a negative electrode containing an iron element.

When K ₂ S is added to the electrolytic solution, there is a problem in that the discharge reactivity is greatly reduced when the concentration of K ₂ S in the electrolytic solution exceeds 0.01 mol / L.
Therefore, when the liquid content in the electrolyte solution by the charging and discharging of the battery is reduced, the concentration of K _{2 S} in the electrolyte increases, the concentration of K _{2 S} in the electrolyte exceeds 0.01 mol / L, the discharge Reactivity (discharge capacity) is significantly reduced. In order to prevent a reduction in discharge capacity, there is a problem that it is necessary to perform highly accurate concentration control during charging and discharging.
In addition, there is a problem that it is difficult to provide a battery with stable quality due to the influence of variation in the concentration of the discharge reaction accelerator during the preparation of the electrolytic solution.
It is considered that sulfide ions are adsorbed on the surface of the iron negative electrode, thereby suppressing iron repassivation and suppressing hydrogen generation during charging. Therefore, it is presumed that the amount of sulfide ions adsorbed on the iron negative electrode surface increases and the sulfide ion adsorption force is strong because the concentration of K ₂ S increases. As a result, it is presumed that the discharge reaction of iron (iron elution reaction) was inhibited and the discharge reactivity was lowered.
The present inventors have made intensive studies in order to solve the above problems, SCN ^- _anion, S ^{₂ O 3 2-} anions, _{and, (CH} 3) 2 NCSS ^- at least one anion selected from the group consisting of anionic It has been found that the discharge capacity of the iron-air battery can be stably improved by adding a discharge reaction accelerator containing selenium to the electrolyte without performing highly accurate concentration control. Specifically, even if the concentration of the discharge reaction accelerator in the electrolytic solution exceeds 0.01 mol / L, the discharge reactivity is stabilized (the discharge capacity does not decrease). Therefore, the influence of variation in the concentration of the discharge reaction accelerator during the preparation of the electrolytic solution can be suppressed. Furthermore, it is possible to suppress a decrease in discharge capacity accompanying an increase in the concentration of the discharge reaction accelerator due to a decrease in the amount of electrolyte during charging and discharging. Among these, Na ₂ S ₂ O ₃ was confirmed to have a higher discharge capacity improvement effect than K ₂ S in addition to having a discharge capacity stabilization effect.
When SCN ^- anion, S ₂ O ₃ ^2- anion, and (CH ₃ ) ₂ NCSS ^- anion are included, the anion preferentially adsorbs on the surface of iron rather than dissolved oxygen in the electrolyte. The anion promotes dissolution of iron as a chelating agent. As a result, it is estimated that precipitation (repassivation of iron) due to excess iron ion saturation concentration on the negative electrode surface is suppressed and an active surface state is maintained.

The aqueous solution contains at least a discharge reaction accelerator and an electrolyte compound.
The discharge reaction accelerator, SCN ^- _anion, S ^{₂ O 3 2-} anions, _{and, (CH} 3) 2 NCSS ^- not particularly limited as long as it contains at least one anion selected from the group consisting of anionic, it preferably contains S ^₂ O ₃ ^2- anions.
Specific examples of the cation contained in the discharge reaction accelerator include Li ⁺ , K ⁺ , Na ⁺ , Rb ⁺ , Cs ⁺ , and Fr ⁺ , and K ⁺ and Na ⁺ are preferable. The cation contained in the discharge reaction accelerator is a cation of a metal that is electrochemically less basic than iron. Therefore, the cation hardly reacts with iron, which is a negative electrode metal, in the electrolytic solution. Therefore, if it is the said cation, it will be hard to inhibit the preferential adsorption | suction of the said anion to iron contained in a negative electrode metal for discharge reaction promotion.
Specific examples of the discharge reaction accelerator include Na ₂ S ₂ O ₃ , NaSCN, and (CH ₃ ) ₂ NCSSNa, and Na ₂ S ₂ O ₃ is preferable.
The content of the discharge reaction accelerator contained in the electrolytic solution is not particularly limited, but is preferably 0.005 mol / L or more and 0.1 mol / L or less.

The electrolyte compound is not particularly limited as long as it has solubility in water and expresses desired ionic conductivity, but the aqueous solution is preferably neutral or basic. From the viewpoint of improving reactivity, those that are basic are particularly preferred.
The electrolyte compound preferably contains at least one metal selected from the group consisting of Li, K, Na, Rb, Cs, Fr, Mg, Ca, Sr, Ba, and Ra. Specific examples of the electrolyte compound include LiCl, NaCl, KCl, MgCl ₂ , CaCl ₂ , LiOH, KOH, NaOH, RbOH, CsOH, Mg (OH) ₂ , Ca (OH) ₂ , and Sr (OH) _2. NaOH and KOH are preferable, and KOH is particularly preferable.
The concentration of the electrolyte compound is not particularly limited, but the lower limit is preferably 0.01 mol / L or more, particularly 0.1 mol / L or more, more preferably 1 mol / L or more, and the upper limit is preferably 20 mol / L or less. In particular, it is 10 mol / L or less, and further 8 mol / L or less.
When the concentration of the electrolyte compound is less than 0.01 mol / L, the solubility of the negative electrode metal may be reduced. On the other hand, when the concentration of the electrolyte compound exceeds 20 mol / L, the self-discharge of the iron-air battery is accelerated, and the battery characteristics may be deteriorated.
The pH of the electrolytic solution is preferably 7 or more, more preferably 10 or more, and particularly preferably 14 or more.

2. Iron-air battery The iron-air battery of the present invention includes an air electrode to which oxygen is supplied,
A negative electrode containing iron element;
An electrolyte solution in contact with the air electrode and the negative electrode,
The electrolytic solution is the iron-air battery electrolytic solution.

  In the present invention, an iron-air battery is an electrolytic solution in which a reduction reaction of oxygen, which is an active material, is performed in an air electrode, and an iron oxidation reaction is performed in a negative electrode, and is disposed between the air electrode and the negative electrode. Refers to a battery through which ions are conducted. The iron-air battery of the present invention may be a primary battery or a secondary battery.

FIG. 1 is a cross-sectional view showing a schematic configuration of an iron-air battery of the present invention.
As shown in FIG. 1, the iron-air battery 10 holds a negative electrode 11, an air electrode 12 provided separately from the negative electrode 11, and an electrolyte solution 13 disposed between the negative electrode 11 and the air electrode 12. Part of the outer package 17, a separator 14 that is connected to the negative electrode 11, an air electrode current collector 16 that is connected to the air electrode 12, and an outer package 17 that accommodates these. Is formed of a water repellent film 18. The iron-air battery 10 is configured so that the electrolytic solution 13 does not leak from the exterior body 17 using a water repellent film 18 or the like.

  Since the electrolytic solution that can be used in the iron-air battery of the present invention is the same as the above-mentioned “1.

The iron-air battery of the present invention has a separator for ensuring the insulation between the air electrode and the negative electrode as necessary. It is preferable that a separator has a porous structure from a viewpoint of hold | maintaining electrolyte solution. The porous structure of the separator is not particularly limited as long as the electrolyte solution can be retained. For example, the separator has a mesh structure in which constituent fibers are regularly arranged, a nonwoven fabric structure in which constituent fibers are randomly arranged, independent holes, and connecting holes. Examples include a three-dimensional network structure. A conventionally well-known thing can be used for a separator. Specific examples include porous films such as polyethylene, polypropylene, polyethylene terephthalate, and cellulose, and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric.
The thickness of a separator is not specifically limited, For example, the range of 0.1-100 micrometers is preferable.
The porosity of the separator is preferably 30 to 90%, and more preferably 45 to 70%. If the porosity is too low, ion diffusion tends to be inhibited, and if it is too high, the strength tends to decrease.

The air electrode includes at least a conductive material.
The conductive material is not particularly limited as long as it has conductivity, and examples thereof include a carbon material, a perovskite-type conductive material, a porous conductive polymer, and a metal body.
The carbon material may have a porous structure or may not have a porous structure, but preferably has a porous structure. This is because the specific surface area is large and many reaction fields can be provided. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon black, carbon nanotube, and carbon fiber.
A metal body can be comprised with the well-known metal stable with respect to electrolyte solution. Specifically, for example, the metal body has a metal layer (coating film) containing at least one metal selected from the group consisting of Ni, Cr, and Al formed on the surface, The whole may be composed of a metal material made of at least one metal selected from the group consisting of Ni, Cr, and Al. The form of the metal body can be a known form such as a metal mesh, a metal foil that has been punched, or a metal foam body.
As content of the electroconductive material in an air electrode, when the mass of the whole air electrode is 100 mass%, for example, it is preferable that it is 10-99 mass%, especially 50-95 mass%.

The air electrode may contain a catalyst that promotes an electrode reaction, and the catalyst may be supported on the conductive material.
As the catalyst, a known catalyst having an oxygen reducing ability that can be used in an iron-air battery can be appropriately used. Examples of the catalyst include at least one metal selected from the group consisting of ruthenium, rhodium, palladium, and platinum; a perovskite oxide containing a transition metal such as Co, Mn, or Fe; a porphyrin skeleton or a phthalocyanine skeleton. Examples thereof include metal coordination organic compounds having inorganic ceramics such as manganese dioxide (MnO ₂ ) and cerium oxide (CeO ₂ ); and composite materials obtained by mixing these materials.
For example, the content of the catalyst in the air electrode is preferably 0 to 90% by mass, and more preferably 1 to 90% by mass, when the mass of the entire air electrode is 100% by mass.

The air electrode contains a binder for immobilizing the conductive material as necessary.
Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene / butadiene rubber (SBR), and the like.
Although content of the binder in an air electrode is not specifically limited, For example, when the mass of the whole air electrode is 100 mass%, it is preferable that it is 1-40 mass%, and 10-30 mass. % Is particularly preferred.

Examples of the method for producing the air electrode include a method in which the air electrode material such as a conductive material is mixed and rolled, and a method in which a slurry containing the air electrode material and a solvent is applied. Examples of the solvent used for preparing the slurry include acetone, ethanol, N-methyl-2-pyrrolidone (NMP), and the like. Examples of the slurry application method include a spray method, a screen printing method, a gravure printing method, a die coating method, a doctor blade method, and an ink jet method. Specifically, the slurry can be applied to an air electrode current collector or carrier film, which will be described later, and then dried, and the air electrode can be formed by rolling and cutting as necessary.
Although the thickness of an air electrode changes with uses of an iron air battery etc., it is preferable to exist in the range of 2-500 micrometers, for example in the range of 30-300 micrometers especially.

The iron-air battery of the present invention has an air electrode current collector that collects the air electrode as necessary. The air electrode current collector may have a porous structure or a dense structure as long as it has a desired electronic conductivity, but it may diffuse air (oxygen). From the viewpoint of property, those having a porous structure such as a mesh shape are preferable. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. The porosity of the current collector having a porous structure is not particularly limited, but is preferably in the range of 20 to 99%, for example.
Examples of the material for the air electrode current collector include metal materials such as stainless steel, nickel, aluminum, iron, titanium, copper, gold, silver and palladium, carbon materials such as carbon fiber and carbon paper, and high electrons such as titanium nitride. Examples thereof include conductive ceramic materials.
Although the thickness of an air electrode electrical power collector is not specifically limited, For example, it is preferable that it is 10-1000 micrometers, especially 20-400 micrometers. Moreover, the exterior body mentioned later may have the function as an air electrode electrical power collector.
The air electrode current collector may have a terminal serving as a connection portion with the outside.

The negative electrode contains at least a negative electrode active material.
Examples of the negative electrode active material include iron metal, iron alloy, and iron compound, and iron metal is preferable.
Examples of the iron alloy include an alloy with a metal material selected from the group consisting of vanadium, silicon, aluminum, magnesium, zinc, and lithium. The metal other than iron constituting the iron alloy is one kind or two or more kinds. But you can.
Examples of the iron compound include FeO, Fe ₃ O ₄ , Fe ₂ O ₃ , FeOOH, Fe (OH) ₂ , Fe (OH) ₃ , iron (III) nitrate, iron (III) chloride oxide, iron oxalate ( III), iron (III) bromide, iron (III) iodide and the like.
The purity of iron when the negative electrode is iron metal is not particularly limited. The lower limit of the elemental ratio of iron contained in the iron metal is preferably 50% or more, particularly 80% or more, more preferably 95% or more, and especially 99.5% or more. Further, the upper limit of the element ratio of iron contained in the iron metal may be 100% or less, 99.999% or less, 99.99% or less, 99 It may be 9% or less.
The iron alloy preferably has an iron content of 50% by mass or more when the mass of the entire alloy is 100% by mass.
The shape of the negative electrode is not particularly limited, and examples thereof include plates, bars, particles, and mesh shapes. In addition, the particle diameter of the particles when the shape is particulate is preferably 1 nm or more, particularly 10 nm or more, more preferably 100 nm or more as the lower limit, and the upper limit is 100 mm or less, particularly 10 mm or less, and further 1 mm or less. Preferably there is.
The average particle diameter of the particles in the present invention is calculated by a conventional method. An example of a method for calculating the average particle size of the particles is as follows. First, a transmission electron microscope (hereinafter referred to as TEM) with an appropriate magnification (for example, 50,000 to 1,000,000 times), an image or a scanning electron microscope (hereinafter referred to as SEM). In the image, for a certain particle, the particle diameter when the particle is regarded as spherical is calculated. Calculation of the particle size by such TEM observation or SEM observation is performed for 200 to 300 particles of the same type, and the average of these particles is taken as the average particle size.

  The negative electrode contains at least one of a binder that immobilizes the conductive material and the negative electrode active material, as necessary. For example, when the negative electrode active material is plate-shaped, a negative electrode containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder (sphere) shape, a negative electrode containing at least one of a conductive material and a binder and the negative electrode active material can be obtained. In addition, about the kind and usage-amount of an electroconductive material, the kind and usage-amount of a binder, it can be made to be the same as the content described in the air electrode mentioned above.

The iron-air battery of the present invention includes a negative electrode current collector that collects current from the negative electrode as necessary. The material for the negative electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, copper, and carbon. Examples of the shape of the negative electrode current collector include a foil shape, a plate shape, and a mesh shape. Although the thickness of a negative electrode collector is not specifically limited, For example, it is preferable that it is 10-1000 micrometers, especially 20-400 micrometers. Moreover, the exterior body mentioned later may have the function as a negative electrode collector.
The negative electrode current collector may have a terminal serving as a connection portion with the outside.

The iron-air battery of the present invention usually has an exterior body that houses an air electrode, a negative electrode, an electrolytic solution, and the like.
Examples of the shape of the exterior body include a coin type, a flat plate type, a cylindrical type, and a laminate type.
The material of the exterior body is not particularly limited as long as it is stable to the electrolytic solution, but a metal body including at least one selected from the group consisting of Ni, Cr, and Al, and polypropylene, polyethylene, and acrylic resin And the like. When the exterior body is a metal body, only the surface of the exterior body may be composed of a metal body, or the entire exterior body may be composed of a metal body.
The exterior body may be an air release type or a sealed type. The atmosphere-opening exterior body has a hole for taking in oxygen from the outside, and has a structure in which at least the air electrode can sufficiently come into contact with the atmosphere. The oxygen uptake hole may be provided with an oxygen permeable film, a water repellent film or the like. The sealed battery case may have an oxygen (air) introduction pipe and an exhaust pipe.
The water repellent film is not particularly limited as long as the electrolyte does not leak and the air can reach the air electrode. Examples of the water repellent film include porous fluororesin sheets (PTFE and the like), porous cellulose subjected to water repellent treatment, and the like.
Examples of the oxygen-containing gas supplied to the air electrode include air, dry air, pure oxygen, and the like. Dry air and pure oxygen are preferable, and pure oxygen is particularly preferable.

Example 1
First, an 8 mol / L aqueous solution of KOH (manufactured by Wako Pure Chemical Industries, Ltd.) was prepared. And the said aqueous solution was hold | maintained for 8 hours at 25 degreeC in thermostat: LU-113 (made by ESPEC Corporation). Then, as a discharge reaction accelerator _was added Na ₂ S ₂ O 3 a (Aldrich Co.) in the aqueous solution so that 0.01 mol / L. Next, the aqueous solution was stirred with an ultrasonic cleaner for 15 minutes. And the said aqueous solution was hold | maintained at 25 degreeC for 3 hours in the thermostat, and the electrolyte solution for iron-air batteries was obtained.

(Example 2)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that Na ₂ S ₂ O ₃ was added to the aqueous solution as a discharge reaction accelerator at 0.05 mol / L.

(Example 3)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that Na ₂ S ₂ O ₃ was added to the aqueous solution as a discharge reaction accelerator so as to be 0.1 mol / L.

Example 4
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that NaSCN (manufactured by Aldrich) was added to the above aqueous solution as a discharge reaction accelerator at 0.005 mol / L.

(Example 5)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that NaSCN was added to the aqueous solution as a discharge reaction accelerator so as to be 0.01 mol / L.

(Example 6)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that NaSCN was added to the aqueous solution as a discharge reaction accelerator at 0.05 mol / L.

(Example 7)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that (CH ₃ ) ₂ NCSSNa (manufactured by Aldrich) was added to the above aqueous solution as a discharge reaction accelerator to 0.005 mol / L. did.

(Example 8)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that (CH ₃ ) ₂ NCSSNa was added to the aqueous solution as a discharge reaction accelerator so as to be 0.01 mol / L.

Example 9
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that (CH ₃ ) ₂ NCSSNa was added to the above aqueous solution as a discharge reaction accelerator at 0.05 mol / L.

(Comparative Example 1)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that the discharge reaction accelerator was not added.

(Comparative Example 2)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that K ₂ S (manufactured by Aldrich) was added to the aqueous solution so as to be 0.01 mol / L as a discharge reaction accelerator.

(Comparative Example 3)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that K ₂ S was added to the aqueous solution so as to be 0.05 mol / L as a discharge reaction accelerator.

(Comparative Example 4)
An electrolytic solution for an iron-air battery was produced in the same manner as in Example 1 except that K ₂ S was added to the aqueous solution as a discharge reaction accelerator at 0.1 mol / L.

[Discharge reaction evaluation]
(Preparation of electrodes)
As a working electrode, 0.8 g of steel wool (Bonstar # 0000, a filling rate of approximately 0.8%, manufactured by Nippon Steel Wool Co., Ltd.) was prepared. And the said steel wool was immersed in acetone and ultrasonic cleaning was performed for 10 minutes.
As a counter electrode, a nickel mesh (100 mesh manufactured by Niraco Co., Ltd.) cut into a size of 30 mm × 30 mm × 1 mm was prepared. And the nickel ribbon (made by Nilaco Co., Ltd.) was welded to the said nickel mesh, and the said nickel ribbon was used as current collection wiring.
As a reference electrode, an Hg / HgO electrode (manufactured by Interchem Corporation) was prepared.
(Production of evaluation cell)
As an electrolytic solution, 25 mL of the electrolytic solutions of Examples 1 to 9 and Comparative Examples 1 to 4 were prepared.
A cell container (volume 30 mL) was prepared, and the working electrode, the counter electrode, and the reference electrode were arranged in the cell container. The said cell container prepared the number (13 pieces) of Examples 1-9 and the electrolyte solution of Comparative Examples 1-4. And 25 mL of each said electrolyte solution was thrown in in each separate cell container. Furthermore, a lid for suppressing volatilization was attached to each of the above cell containers to produce an evaluation cell. The evaluation cell was produced within 10 minutes.

(Measurement of discharge capacity)
The discharge capacity was measured using each evaluation cell using the electrolyte solutions of Examples 1 to 9 and Comparative Examples 1 to 4.
First, the working electrode and counter electrode of the evaluation cell were connected to a potentiostat / galvanostat (Biologic, VMP3). And before discharge, the potential of the working electrode was kept at −1.2 V (vs. Hg / HgO) for 10 minutes, and the oxide film on the iron surface of the working electrode was reduced and removed. Thereafter, a vacuum treatment was performed to remove hydrogen generated between the electrodes. And it discharged with discharge current 23mA. The discharge was performed until the potential of the working electrode became 0 V (vs. Hg / HgO).
The discharge capacity is about −0. 0 after the plateau at the first stage is completed and the potential rises suddenly from −0.9 V (vs. Hg / HgO) at the start of the discharge reaction. It read from the value of 7V (vs.Hg / HgO). Table 1 shows the measurement results of the discharge capacity (specific capacity) per unit mass of the negative electrode active material.

  As shown in Table 1, the specific capacities of the evaluation cells using the electrolytic solutions of Examples 1 to 9 and Comparative Examples 1 to 4 are 120 mAh / g in Example 1, 132 mAh / g in Example 2, and Example 3 121 mAh / g, Example 4 39 mAh / g, Example 5 54 mAh / g, Example 6 46 mAh / g, Example 7 80 mAh / g, Example 8 65 mAh / g, Example 9 73 mAh / G, Comparative Example 1 was 9 mAh / g, Comparative Example 2 was 101 mAh / g, Comparative Example 3 was 13 mAh / g, and Comparative Example 4 was 1 mAh / g.

As shown in Comparative Examples 2 to 4 in Table 1, when K ₂ S is used as the discharge reaction accelerator, the specific capacity greatly decreases when the concentration of K ₂ S in the electrolyte exceeds 0.01 mol / L. I understand that
On the other hand, the discharge reaction accelerator included in Examples 1 to 9 can stably ensure the specific capacity even when the concentration of the discharge reaction accelerator included in the electrolyte exceeds 0.01 mol / L. I understand that I can do it.
As shown in Table 1, it can be seen that the specific capacities of Examples 1 to 9 are 4.3 to 14.7 times higher than that of Comparative Example 1. In addition, it can be seen that the specific capacities of Examples 1 to ₃ using Na ₂ S ₂ O ₃ are 1.19 to 1.31 times higher than the specific capacity of Comparative Example 2 using K ₂ S. .
Therefore, it can be seen that Na ₂ S ₂ O ₃ not only provides stability of the discharge capacity with respect to the concentration but also higher discharge capacity as compared with K ₂ S.
In addition, it is thought that the discharge capacity differs for each anion species because the strength of the adsorption force of the anion to the iron metal surface and the formation state of defects in the adsorption film are different.

DESCRIPTION OF SYMBOLS 10 Iron-air battery 11 Negative electrode 12 Air electrode 13 Electrolytic solution 14 Separator 15 Negative electrode collector 16 Air electrode collector 17 Exterior body 18 Water repellent film

Claims (6)

SCN ^- _anion, S ^{₂ O 3 2-} anions, _{and, (CH} 3) 2 NCSS ^- made from an aqueous solution containing a discharge reaction accelerator containing at least one anion selected from the group consisting of anionic,
The content of the discharge reaction accelerator is 0.005 mol / L or more and 0.1 mol / L or less, and an electrolytic solution for an iron-air battery having an anode containing an iron element. The discharge reaction accelerator includes at least one cation selected from the group consisting of Li ⁺ cation, K ⁺ cation, Na ⁺ cation, Rb ⁺ cation, Cs ⁺ cation, and Fr ⁺ cation. Electrolyte. The electrolytic solution according to claim 1, wherein the discharge reaction accelerator is Na ₂ S ₂ O ₃ . The electrolytic solution according to any one of claims 1 to 3 , wherein the aqueous solution is basic. The electrolyte solution according to any one of claims 1 to 4 , wherein the aqueous solution contains KOH as an electrolyte compound. An air electrode supplied with oxygen;
A negative electrode containing iron element;
An electrolyte solution in contact with the air electrode and the negative electrode,
The iron-air battery, wherein the electrolytic solution is the electrolytic solution according to any one of claims 1 to 5 .